1. Field of the Invention
The present invention relates generally to actuators used in electronic devices, and in particular to tunable matching networks and the circuit topology for such networks.
2. Description of the Related Art
The theory for fixed matching networks has been developed over many decades with fundamental work summarized in Microwave Filters, Impedance-Matching Networks, and Coupling Structures by Matthaei, Young, and Jones.
However, the literature for matching networks that utilize tunable components for matching variable loads and/or optimizing performance at multiple frequencies is not well developed. The fixed network theory focuses on the required matching bandwidth and losses within the network. These requirements can be adapted for the tunable case by only requiring the instantaneous bandwidth at a given operating channel set. To minimize the size and loss of the network, it is preferable to use the minimum number of components. To maximize the upper frequency limit and minimize the product size, it is strongly preferred to use smaller capacitor and inductor element values. Tunable matching networks also require minimizing the insertion loss in the case of the well-matched load. The combination of matching improvements and circuit losses can best be characterized by the transducer gain achievable into the specified load.
Tunable matching networks are useable in cellular telephone handsets, specifically for handset antenna applications. The top-level constraints for matching topology selection are performance, cost and size. Key technology contributors to performance that interact with the topology selection include tunable element ratios (ratio between maximum and minimum values achievable by the element), tunable element parasitics (non-ideal element behavior), tunable element density (reactance per volume), tunable element Q (ratio of reactive power storage to power loss), package dielectric constant, package height, package metal conductivity, package metal thickness, package metal surface finish and package design rules.
It can be seen, then, that there is a need in the art for performance criteria for tunable matching networks. It can also be seen that there is a need in the art to apply the performance criteria to specific topologies to determine the proper topology for a given application of the tunable matching network constrained by a given set of element and package technologies.